1. Field of the Invention
This invention relates generally to a deposition mask or screen, and more particularly to a photoplate for fabricating an OLED deposition screen.
2. Description of the Related Art
The production of Organic Light Emitting Diode (OLED) televisions and other display panels provides many new challenges. One such challenge is deposition of the thin organic material onto the TFT substrate. It is preferable to maximize the coverage area of the pixel relative to the overall area of the picture, which is accommodated by having rectangular pixels with sharp corners.
Organic materials are routinely thermally evaporated and deposited on a cooled substrate through a deposition mask. In the past this mask has been made of electro-deposited nickel. As screen size increases from the current relatively small diagonal (˜3″) used in point and shoot cameras to home displays ranging from 28″ to 70″ or more, the use of an electro-deposited nickel mask provides many processing challenges, many of which are related to the thermal expansion of the material.
Precision metal masks are used in the manufacturing process of making some information displays including Cathode Ray Tubes (CRTs) and OLED displays. Recent increases in screen resolution and sizes are pushing the mask specifications beyond the current capabilities of metal mask production technologies.
One example is the mask needed for depositing material onto a substrate in the production of small molecule OLED screens. The substrate glass has thin film transistors already in place and the OLED material must be deposited in the precise locations on the glass. The positional tolerance of the holes in the deposition mask must meet the requirements after mask manufacturing and during the deposition process.
One way to make metal deposition masks is to chemically etch the holes. This requires several steps to be performed on the metal including cleaning, photoresist coating, imaging, photoresist developing, acid etching, curing substrate protective coating, and resist stripping. These steps cause the mask to be heated and cooled several times during the process. The mask also gets thermally cycled during the process of depositing the organic material onto the substrate.
What is needed are mask designs that accommodate the tolerances and designs required for newer displays, and masks that are dimensionally stable when they are made and in the manufacturing of OLED display screens.